Recently, Near Earth Objects (NEOs) have been attracting great attention, and thousands of NEOs have been found to date. This paper examines the NEOs' orbital dynamics using the framework of an accurate solar system model and a Sun-Earth-NEO three-body system when the NEOs are close to Earth to search for NEOs with low-energy orbits. It is possible for such an NEO to be temporarily captured by Earth; its orbit would thereby be changed and it would become an Earth-orbiting object after a small increase in its velocity. From the point of view of the Sun-Earth-NEO restricted three-body system, it is possible for an NEO whose Jacobian constant is slightly lower than C1 and higher than C3 to be temporarily captured by Earth. When such an NEO approaches Earth, it is possible to change its orbit energy to close up the zero velocity surface of the three-body system at point L1 and make the NEO become a small satellite of the Earth. Some such NEOs were found; the best example only required a 410m/s increase in velocity.

We are a small project with an ambitious goal: early warning of asteroid impact on Earth.We think it's possible to provide a useful degree of warning for most impacts, meaning a day for a 30 kiloton "town killer", a week for a 5 megaton, "city killer", three weeks for a 100 megaton "county killer". (Yes, those are the same kilotons and megatons of TNT used to describe nuclear explosions because a serious asteroid impact is very similar to a nuclear explosion, complete with mushrooom cloud, except there is no radioactivity or fallout.) We also think it's possible to build and operate the system for a relatively small amount of money ($2M construction and $0.5M per year for operations). Read more

At 4:33 a.m. on a recent Friday, Timothy Spahr was startled awake by a beep from his mobile phone: A text message alerted him that a rocky object was hurtling toward Earth. He told his wife it was "some asteroid thing" and went to check his computer.In Hollywood, this would be the opening scene to a doomsday movie. But for Spahr, director of the Minor Planet Centre at the Harvard-Smithsonian Centre for Astrophysics, it is just another day.Read more

Meteorites have had a bad press in recent years. Scientists have linked the crash of a 10km-wide rock 65m years ago with the demise of the dinosaurs, for example. Hollywood sci-fi movies have depicted modern civilisation under threat from huge meteorites plunging towards our planet. Geologist Ted Nield believes this is all too much and his latest book, Incoming!: or, Why We Should Stop Worrying and Learn to Love the Meteorite, attempts to paint our rocky neighbours in a better light.

Title: An Early Warning System for Asteroid ImpactAuthors: John L. Tonry

Earth is bombarded by meteors, occasionally by one large enough to cause a significant explosion and possible loss of life. Although the odds of a deadly asteroid strike in the next century are low, the most likely impact is by a relatively small asteroid, and we suggest that the best mitigation strategy in the near term is simply to move people out of the way. We describe an "early warning" system that could provide a week's notice of most sizable asteroids or comets on track to hit the Earth. This system, dubbed "Asteroid Terrestrial-impact Last Alert System" (ATLAS), comprises two observatories separated by about 100km that simultaneously scan the visible sky twice a night, and can be implemented immediately for relatively low cost. The sensitivity of ATLAS permits detection of 140m asteroids (100 Mton impact energy) three weeks before impact, and 50m asteroids a week before arrival. An ATLAS alarm, augmented by other observations, should result in a determination of impact location and time that is accurate to a few kilometres and a few seconds. In addition to detecting and warning of approaching asteroids, ATLAS will continuously monitor the changing universe around us: most of the variable stars in our galaxy, many micro-lensing events from stellar alignments, luminous stars and novae in nearby galaxies, thousands of supernovae, nearly a million quasars and active galactic nuclei, tens of millions of galaxies, and a billion stars. With two views per day ATLAS will make the variable universe as familiar to us as the sunrise and sunset.

Experts are calling on the world to recognise the "global threat" of an asteroid hit to earth.Scientists and astronauts have been holding a three-day workshop in Germany, discussing how countries would react.Read more

How would the world react to the threat of an asteroid impact? The media are invited to meet top-level experts at ESA's space operations centre in Germany on 29 October to find out more. The media are invited to Darmstadt, Germany for a briefing at the end of a workshop on Near-Earth Objects (NEOs) and the dangers they present. Read more

If a medium-sized asteroid lands in the ocean, tsunamis won't be the only worry. A new computer simulation suggests that the water vapour and sea salt thrown up by the impact could damage the Earth's protective ozone layer, leading to record levels of ultraviolet radiation that could threaten human civilisation.Read more